The present invention relates to a developing apparatus for forming images on a recording medium using powder developer. More specifically, the present invention relates to a compact, high-resolution; high-speed recording developing apparatus suitable for the electrostatic recording device used in electrostatic copy machines, electrostatic printers, electrostatic facsimiles, electrostatic plotters and the like.
The aforesaid electrostatic recording apparatus forms a developer image by electrostatically adhering a powder developer on a recording member such as a photosensitive member, dielectric member or the like, and has found wide application. More specifically, the powder developer may be a bicomponent developer comprising toner particles and carrier particles, or a monocomponent developer comprising only toner particles. Conventional recording devices are practical for utilization in a variety of fields such as, for example, facsimile printers used as output devices for optical communications and computers, but higher performance is desirable due to the current demands of society.
One of these demands is for down-sizing the entire unit into a more compact package. A further demand is for higher density recording images, necessitating improved resolution. Another demand is for higher speed recording.
While down-sizing the entire device is desirable from many perspectives, a developing apparatus adapted for use in conventional electrostatic recording devices agitates and mixes the toner and carrier powders through a mechanically applied external force so as to triboelectrically charge the powders with an electrostatic charge, thus requiring a drive unit for the agitation of the powders which has the inherent disadvantage of preventing down-sizing of the unit beyond a certain degree.
Improvement of the resolution of the recording image, i.e. the developer image on the recording medium, is especially important for recent design utilizing computer capabilities and computer-aided design (CAD) system output devices and the like.
Conventional developing apparatuses, however, use developer which is triboelectrically charged through a mechanically applied external force, as previously described. In concrete terms, a problem arises when the developer is mixed by an agitator or sleeve or the like, in that the toner particles in said developer continually agglomerate and disperse, or the toner particles adhere to carrier particles and the developer cannot achieve the anticipated characteristics.
Further, although it is known that adequate triboelectric charging uniformly charges the developer so as to effectively prevent blurring of the recording image, uniform charging of conventional developers is difficult to accomplish. That is, as the amount of mechanically applied external force used to induce triboelectric charging is increased, the developer loses stress resistance making the, previously described developer agglomeration more probable and leading to disadvantages such as developer particles being randomly dispersed to inappropriate portions of the recording medium.
There have been various approaches to improving image resolution, one of which is the use of small diameter developer particles. That is, extremely small particles having diameters ranging from several .mu.m to 10 .mu.m are used in image formation to improve fine line reproducibility in particular. However, particles of that size have certain drawbacks in that small diameter particles have poor flow characteristics, are difficult to charge triboelectrically due to the difficulty in mixing such particles, and are randomly dispersed outside the target areas, thereby preventing the formation of a high quality developer image.
Further, capsule toner is another well known type of developer Capsule toner comprises an ink component and resin component to achieve permanent fusion of the developer on an appropriate recording medium, but such components are too readily susceptible to fusion and agglomeration and have inherent disadvantages such as the lack of capsule durability due to stress caused by charging via mechanical external force, and damage to said capsule which leads to fusion and agglomeration of the developer.
The demand for high-speed recording has also increased in recent years. To accomplish high-speed recording, it is necessary to increase the volume of developer supplied per unit time. However, certain disadvantages, such as developer scattering, accompany this increase in developer volume deliver.